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Chapter 9
Between-subject design (Bet-Ss) aka “Between-participant design” Experimental design and vocabulary Threats to internal validity Threats to external validity
Within-subject design (W/in-Ss) aka “Correlated-groups designs” Within-participants design or “Repeated measures design” ▪ Participants complete all (2+) conditions. ▪ Researcher examines if difference between means ▪ e.g. pre-post-test, longitudinal study (vs. cross-sectional) ▪ Multiple testing sessions or complete conditions successively
Matched-participants design
Introduction Can we improve memory for nonsense pics w/ cue?
Method Study: See 28 pics (w/ or w/o label) Test: Immediate recall (draw)
Results Label: 70% (SE= 1.25) No label 51% (SE=.92) t(16) = 3.43, p < .01
Discussion Memory significantly improved by use of verbal label
Droodles by Roger Price a. 4 elephants sniffing an orange b. An early bird catching a very strong worm c. A man in a mailbox signaling a left turn
If Bower, Karlin, & Dueck was replicated using a within-subject design, what would it look like?
What is the independent variable (IV)?
What are the levels of the IV?
What is the dependent variable (DV)?
What is measured?
Bet-Ss desgin W/in-Ss design
Ss Group Accuracy
1 no label 50
2 label 90
3 no label 60
4 label 85
5 no label 45
6 label 75
7 no label 30
8 label 90
Ss Acc-Label Acc-NoLabel
1 90 50
2 85 60
3 75 45
4 90 30
MORE data from fewer Ss!!
05
101520253035404550
Nonsense Rare Common Color-
Associated
Similar
Color-Word
Incongruent
Color-Word
Interference (Seconds)
Co
nd
itio
ns
Inte
rfe
ren
ce
(s
)
Condition
Stroop experiment: “say color of stimulus”
IV: condition (separate groups of Ss)
Duke undergraduates tested day after 9/11 (Flashbulb memory - FB)
Tested again at 1, 6, or 32 weeks after 9/11
DV: consistency of FB and everyday memory
Results: Both types of memory declined over time
No relationship between accuracy and confidence in memory
Method IV: group (training vs. no training) IV: Training - 12+ days on working memory task
“n-back” http://brainworkshop.sourceforge.net/
DV: Performance on intelligence task before and after training sessions
Method: Baseline task:
Find repeated # in series of 10 #s
Transformation task:
Add or subtract 1 to each #, then find repeated # in series of 10 #s
IV: Age (Yng v Older) DV: Accuracy
0.00
0.20
0.40
0.60
0.80
1.00
Baseline TransformationTask conditions
Accu
racy
Yng
Older
PRO
Need fewer Ss (compared to bet-Ss)
Or get more data!
Can take less time If all conditions are in 1 session rather than separate sessions for each Ss
Increases POWER Decreases variability
Less individual differences so more likely effect is due to IV not b/c Ss in grps are different
CON
Testing effects Fatigue effect
Practice effect
Order effect Carry-over effects (“transfer”)
1st condition affects performance in 2nd condition
e.g. knowledge, attitude, etc. Increase in demand
characteristics aka “participant effects”
Ss has more info about the study so can change behavior
Distribute potential order effects evenly over groups by using counterbalancing techniques
If use w/in-Ss design for Bower, Karlin & Dueck ½ Ss receive label then no-label condition ½ Ss receive no label then label condition
Complete counterbalancing If 4 conditions = 24 possible orders!
Partial counterbalancing Randomly select orders to use
Latin squares design Same # orders as # of conditions Each condition presented at each order\ E.g. 3 conditions: ABC / BCA / CAB
Gil Einstein @ Furman University
Event-based vs. time-based PM
Einstein & McDaniel (1990)
Question: What is effect of cue familiarity on PM
Method: Press key when see cue word
Results: 3x more likely to press key for unfamiliar cue word than familiar cue word
Kliegel et al (2004)
How likely are you to forget PM task? - Effect of background task - Effect of importance
Use separate groups of Ss for each condition BUT, Ss for each condition are similar What variables should Ss be matched on? How many variables should Ss be matched on?
It depends on the study!
Used (more often) in clinical or drug research
Match based on:
Person variables (gender, age, ethnicity)
Others such as intelligence, socioeconomic status
Can also use “natural pairs” such as twins
Ss fill-out “test of language ability”
Unknowingly “primed” w/ stereotypes of words in 1 of 3 categories
Examine how quickly Ss interrupts conversation of experimenter w/ friend
PRO
Eliminate testing effects (carry-over or order effects)
Reduce demand characteristics (participant effects)
Less variability among Ss compared to traditional bet-Ss design so increases power
Can use statistics for w/in Ss design so there is more power than bet-Ss design
CON
Need more Ss compared to w/in-Ss design
If loose 1 Ss from one group, loose matched Ss in other group (pair-wise loss)
Need to decide what & # of characteristics to match Ss on
Difficult to find matches (especially if mult. charcts)
Reduces benefit of random selection (can loose benefit of random assignment)
College students rate pronounceability of famous and non-famous male and female names
Later (24hrs/48hrs) judged whether each name was famous or not
50
55
60
65
70
75
80
Familiar M Familiar F Unfamiliar M Unfamiliar F
Per
cen
t hits
Male
Female
74%
65% 68%
61%
0
2
4
6
8
10
Familiar M Familiar F Unfamiliar M Unfamiliar F
Per
cent
fal
se a
larm
s
Nonequivalent control grp Use random assignment Use pretest/posttest design
History Test at different time pts
Maturation Use control group
Testing effect Use control group
Regression to mean Use control grp w/ same extreme scores
Instrumentation effect Use control group
Mortality or attrition Use control group
Diffusion of treatment Tell Ss not to discuss study
Experimenter or participant effects
Use single-blind or double-blind method Use placebo group
Ceiling and floor effects Carefully select DV to avoid
How to prevent these potential confounds